Tungsten-copper (W--Cu) pseudoalloys are used in the manufacture of electrical contact materials and electrodes, thermal management devices such as heat sinks and spreaders, and conductive inks and pastes for ceramic metallization. The basic methods for the fabrication of articles composed of W--Cu pseudoalloys include: infiltration of a porous tungsten skeleton with liquid copper, hot pressing of blends of tungsten and copper powders, and various techniques incorporating liquid phase sintering, repressing, explosive pressing, and the like. Complex shapes may be made by injection molding W--Cu composite powders. It is desirable to be able to manufacture articles made from W--Cu pseudoalloys at or near the theoretical density of the pseudoalloy. Besides having improved mechanical properties, the higher density pseudoalloys have higher thermal conductivities which are critical for the application of W--Cu pseudoalloys as heat sink materials for the electronics industry.
The components in the W--Cu system exhibit only a very small intersolubility. Thus, the integral densification of W--Cu pseudoalloys occurs above 1083.degree. C. in the presence of liquid copper. The compressive capillary pressure generated by the forming and spreading of liquid copper, the lubrication of tungsten particles by liquid copper and the minute solubility of tungsten in copper above 1200.degree. C. combine to cause the relative movement of tungsten particles during sintering and thereby make possible the displacement of tungsten particles. Local densification and rearrangement of the tungsten framework causes an inhomogenous distribution of W and Cu phases in the sintered article and copper bleedout, i.e. the loss of copper from the sintered article. This leads to the degradation of the thermal/mechanical properties of the sintered article.
Prior art methods directed to improving the homogeneity of W--Cu composite powders by coating tungsten particles with copper have not been successful as these copper-coated powders still exhibit a high tendency towards copper bleedout during the consolidation of the composite powder into fabricated shapes.
Thus, it would be advantageous to eliminate copper bleedout from occurring during the liquid-phase sintering of W--Cu pseudoalloys while providing a homogeneous distribution of W and Cu phases in the sintered article.